In the prior art, systems are known for the recording and the reproduction of sound. Such systems provide, with an array of loudspeakers, the physical reconstruction of a desired sound field over a region of space. The sound field generated by the loudspeakers should give to the listeners located in the listening area the realistic perception of a desired virtual sound source or of a virtual sound scene.
One well known technology of this kind is Wave Field Synthesis disclosed in patent applications US 2006/0098830 A1, WO2007/101498 A1, US 2005/0175197 A1, US 2006/0109992 A1, for example. The technology uses the Kirchhoff Helmholtz equation which implies, in theory, the use of both dipole-like and monopole-like secondary sources (the loudspeakers), the strength of which (that are proportional to the loudspeaker signals) is explicitly given by the value of the sound field on the integration contour and its normal derivative, respectively.
Another known technology is Ambisonics, for example as disclosed in U.S. Pat. No. 5,757,927—1998, High Order Ambisonics as disclosed in US 2006/0045275 A1 and another technology disclosed in US 2005/0141728 A1. The theoretical formulation of these methods involve a large use of cylindrical or spherical harmonics and Legendre polynomials, in the same way that the use of sines and cosines or complex exponentials arise in the theoretical formulation of any technology based on the traditional Fourier transform. These prior art technologies involve the use of a matrix-based processing to encode the recorded signals and generate an intermediate format, and a matrix-based system to decode this intermediate format and generate the driving signals for the loudspeakers.
We seek to provide an improved apparatus and method for reproduction of sound.